1. Field of the Invention
The present invention is related generally to a method for detecting secondary particles triggered by a primary particle beam using a detector system with at least one region sensitive to the secondary particles and an extraction and/or deflection field, as well as to an arrangement to implement such method.
2. Description of the Related Art
When a primary particle beam impinges a substrate, then secondary particles are emitted due to the interaction of the primary particles with the substrate. The energy distribution and angular distribution of the secondary particles depends on, among other things, the chemical and physical composition present at the region of interaction, the surface structure, and the voltage distribution present at the specimen. The secondary particles that are triggered in near-surface regions are of particular importance for imaging the surface structures and the distribution of electrical potential using a scanning electron microscope. The secondary electrons are usually detected with a detector arranged laterally of the specimen to be investigated. As a consequence of the asymmetrical arrangement of the detector within a specimen chamber, the detection probability of the secondary electrons is greatly dependent on their emission angle. The detector of the known device is usually formed of an extraction grid, a scintillator, and a photomultiplier coupled by a light guide.
A detector system having a plurality of secondary electron detectors arranged symmetrically relative to a specimen is disclosed in European Pat. No. 0 018 031. The multi-detector system is predominantly used for investigating large specimens to guarantee a largely symmetrical extraction of the secondary electrons independent of the emission point and emission angles. Symmetrical detector arrangements, however, have an important disadvantage in that the secondary electrons emitted nearly in the direction of the symmetry axis of the system are only slightly deflected due to the negligible strength of the extraction field in this region. Thus, such secondary electrons are not documented. As a consequence of the cosine distribution of the exit angle of the secondary particles, however, the probability that secondary electrons will be emitted in the direction of the symmetry axis of the detector arrangement is very high.